1. Field of the Invention
The invention relates to a gripper control for sheet grippers on a sheet-guiding cylinder or the like in a printing press, wherein a stationary pressure generator for a pressure medium is connected by means of a coupling, through the intermediary of a servo-valve actuatable by a motor, to a sheet-gripper actuating system disposed on the cylinder or the like and being acted upon by the pressure medium through a control system, in time with an operating cycle of the printing press.
2. Description of the Related Art
Such a gripper control has become known heretofore from German Published Non-Prosecuted Patent Application (DE-OS) 23 02 519. A pressure generator, not otherwise described in any greater detail in this publication, is connected via a servo-valve, which is adjusted by means of a driven cam plate, through the intermediary of a tube coupling in the form of a rotary connector, to a sheet-gripper actuating system disposed on the cylinder and formed of a diaphragm member acted upon by the pressure medium, and of a spring element.
Compared with all-mechanical gripper controls, such a gripper control reduces the moving masses and therefore also the reaction of controlling and inertial forces on the main drive of the printing press. The cam plate permits the rotational speed-dependent time response of the gripper control to be controlled only to an inadequate extent, unless every conceivable printing-press speed were to be associated with its own cam plate. An adjustable cam plate according to claim 3 of the aforementioned publication would have to have a correspondingly costly, rotational speed-dependent control, the outlay for which does not, however, justify any resultant benefits derivable therefrom.
Heretofore known from German Patent 21 13 750 is a magnetically actuatable sheet gripper wherein a gripper finger is moved into a closed position by an electromagnet against the force of a spring. Reliable operation for in-register sheet gripping and transfer within a wide rotational-speed range is not achievable due to rotational speed-dependent switching delays, which have an effect upon the closing of the gripper.
It has also become known heretofore from German Published Prosecuted Patent Application (DE-AS) 11 00 043 to connect a gripper finger of a relatively simple gripper system to an hydraulically or pneumatically operated piston-cylinder unit and to actuate the latter by means of a valve controlled by a cam. Accurate sheet gripping is not provided for with this heretofore known arrangement.
It is accordingly an object of the invention to provide an improvement in the gripper control of the type initially described in the introduction hereto and to further improve the action thereof through the use of electronic control features.